Start on Petrol or LPG?

[Cannon]

Hi all,

I have SVI on my 2003 V8 which starts on petrol then switches to LPG when it warms up.

Just wondering what the benefits of starting like this are as opposed to starting on LPG?

[bee utey]

Hi all,

I have SVI on my 2003 V8 which starts on petrol then switches to LPG when it warms up.

Just wondering what the benefits of starting like this are as opposed to starting on LPG?

It's mainly about meeting emissions, a warm converter functions more reliably than a cold one, meeting euro emissions specs better. It also stops the risk of flooding the engine with excess gas from a cold converter if the engine is shut down too soon. Basically it's idiot proofing. I've had to raise the temp for changeover for a couple of vehicles as changeover coincided with the end of their driveway or a major downhill intersection and stalling/rough running resulted.

Some systems have an emergency over-ride procedure to allow cold starting on gas, in case the petrol system is faulty. If your system has a push button for change over try holding down the button before the gauge lights come on, crank it with the button still down, see if it starts on gas. It may run a bit rough as the fine settings for cold running aren't there.

[Cannon]

Thanks mate:)

It does start on gas by holding the button in.

I like idiot proof just wondering

[Deltacharliepapa]

i had long reach ute on gas, and my mechanic all ways told me to start it on petrol. cant remember why tho.
super useful post i know. :p

[ozscott]

I dont think my BRC-Impco injected system has an emergency LPG start...

Cheers

[ian4002000]

The last couple of ford utes I owned, where very difficult to start on gas, It was much easier to start on petrol and then use gas for the rest of the trip.
The benefits are also that its keeps the petrol fresher if you use some occasionally, this stops corrosion in the tank with water collecting.
The engines also have little wear on gas and thus running on petrol when cold beds the rings and keeps the bores in better shape.
I had a lot of trouble when using ethanol petrol in duel fuel applications due to the fuel going stale very quickly, it cost me a fuel pump real quick, since then I only put the real petrol in duel fuel cars.
It is also good to keep at least a quarter of a tank of petrol in a lot of late model cars, if the fuel pump is located in the tank it is cooled by the fuel, if the tank is empty your fuel pump may overheat ....

[bee utey]

Mixer type dual fuel systems on EFI vehicles generally start with a short burst of petrol. If they don't start well on LPG the petrol timer is likely out of adjustment or incorrectly set up. Running a dual fuel engine on petrol when cold is only shortening its life. Rings don't need bedding in each morning. My wife's old P76 did 400,000km on straight LPG and still has perfect compression figures. It also started easily when cold every day because of the right choice of high energy ignition and plug gap adjustment.

[UncleHo]

My old 85 carby Rangie starts on LPG from cold even if it has been sitting for a week,I have to remember not to touch the pedal as I do in my series or it is a petrol start run for a few K's switch all fuel off & run the carbies dry and switch to LPG as the engine dies,as I was instructed to do all those years ago.

[loanrangie]

My old 85 carby Rangie starts on LPG from cold even if it has been sitting for a week,I have to remember not to touch the pedal as I do in my series or it is a petrol start run for a few K's switch all fuel off & run the carbies dry and switch to LPG as the engine dies,as I was instructed to do all those years ago.

Both my old 81 and 85 rangies were the same, i usually did the fuel changeover on the highway if possible or coasting, except i used to floor it from cold to start it on lpg with the old impco system fitted.

[Pedro_The_Swift]

The gentleman the built my new 4.6 told me to run it on ULP often.
It runs on ULP every time I start it,,
maybe he didnt know that,, but I still wonder why he would say that,,,:confused:

[TheTree]

Mixer type dual fuel systems on EFI vehicles generally start with a short burst of petrol. If they don't start well on LPG the petrol timer is likely out of adjustment or incorrectly set up. Running a dual fuel engine on petrol when cold is only shortening its life. Rings don't need bedding in each morning. My wife's old P76 did 400,000km on straight LPG and still has perfect compression figures. It also started easily when cold every day because of the right choice of high energy ignition and plug gap adjustment.

Hi

Mine runs for a couple of minutes at least usually, though very occasionally seems much quicker.

I will try holding down the button and see if it starts on LPG

Steve

[bee utey]

The gentleman the built my new 4.6 told me to run it on ULP often.
It runs on ULP every time I start it,,
maybe he didnt know that,, but I still wonder why he would say that,,,:confused:
I class that as one of the "old mechanics tales". There is a tiny little truth in the assertion that you need to bed in a set of chrome rings on petrol because it weakens the lubrication on the cylinder walls. What kind of deal is that? Either make sure the rings are bedded in properly or fit rings suitable for 100% LPG use. I've rebuilt a few engines in my time and never run a drop of petrol through them for running in purposes. A hard fang up the local mountain and they're all good, for 420,000km in a P76 and in an XF taxi with well over 600,000km.

[TheTree]

HI

Mine says to run a 100Ks or so every couple of months, I believe it has something to do with keeping the cat converters happy.

Bedding in the rings is nonsense, LPG certainly produces less wear

Steve

[bee utey]

HI

Mine says to run a 100Ks or so every couple of months, I believe it has something to do with keeping the cat converters happy.

Bedding in the rings is nonsense, LPG certainly produces less wear

Steve

Actually it has nothing to do with the cat converters. It has to do with the petrol system as a whole. Old petrol can do damage as it loses its lighter fractions to evaporation and any moisture dissolved with the fuel will accumulate unless you replace the fuel regularly. I don't normally suggest a specific usage distance, other than to make sure you have substantially fresh fuel in the petrol tank within three months at the latest. Either use it up or siphon it out for use in someone else's petrol powered machine. Overly old petrol will be hard to start and possibly very low in octane, apart from damaging injectors. I had a shocker come in last month, the petrol was a year old and pinged like crazy when it had warmed up enough to run on the degraded fuel.

[BigBadBrad]

Starting on petrol has a few benefits and one of them is making you keep fresh fuel in the tank, but fuel as in petrol is obviously a liquid and does have upper cylinder and fuel pump and line lubricating properties. Starting and stopping on petrol keeps these components lubricated especially on carby vehicles. LPG in most systems is introduced to the system as a vapour which is dry and will cause seals to dry out over time. I had to rebuild many a carby for this reason. As for emissions, LPG burns cleaner than petrol hence rarely seeing LPG blowing smoke unless the oil is bypassing the piston rings. I have always started and stopped my dual fuel cars this way and have never had to repair any carby or fuel pumps for this reason in my own cars.

[Blknight.aus]

screw that noise.

It looks after your fuel rail and injectors by ensureing that there is always fresh fuel in the rail and injectors and that your petrol system works if you need it when you run out of LPG.

ever seen the end result of modern fuels being cooked inside an engines fuel system, remember the gum that used to come in carbies that had these massive holes in them called main jets and idle jets that used to cause problems.

Imagine that with holes that are on average something like 10-20 times smaller than those holes...

addidionally LPG will freeze in the converter causing sporadic running at best and continual stalls until the engine warms up. If you start on petrol usualy after 5-10 minutes theres enough heat to prevent this.


everything else is just an added benefit that keeps the greenies happy.

[bee utey]

screw that noise.

It looks after your fuel rail and injectors by ensureing that there is always fresh fuel in the rail and injectors and that your petrol system works if you need it when you run out of LPG.

ever seen the end result of modern fuels being cooked inside an engines fuel system, remember the gum that used to come in carbies that had these massive holes in them called main jets and idle jets that used to cause problems.

Imagine that with holes that are on average something like 10-20 times smaller than those holes...

addidionally LPG will freeze in the converter causing sporadic running at best and continual stalls until the engine warms up. If you start on petrol usualy after 5-10 minutes theres enough heat to prevent this.


everything else is just an added benefit that keeps the greenies happy.

:eek:

Either there's a whole lot of dodgy gas installers out your way or no-one's there has ever figgered how to operate a gas car. I've been doing gas installs for 30 years and always start on gas in the coldest conditions, drive gently until the temp gauge is off the bottom stop, then give it heaps if appropriate. Petrol cold starts wash oil off the cylinder bores, foul cold running plugs and blacken the oil. I tell people to save their petrol for a warm engine and give it a decent run on the expensive stuff once a week. That's apart from the straight gas cars I've done that go for hundreds of thousands of kays without ever seeing a drop of the stinky liquid.:p

[Collins]

screw that noise.

It looks after your fuel rail and injectors by ensureing that there is always fresh fuel in the rail and injectors and that your petrol system works if you need it when you run out of LPG.

ever seen the end result of modern fuels being cooked inside an engines fuel system, remember the gum that used to come in carbies that had these massive holes in them called main jets and idle jets that used to cause problems.

Imagine that with holes that are on average something like 10-20 times smaller than those holes...

addidionally LPG will freeze in the converter causing sporadic running at best and continual stalls until the engine warms up. If you start on petrol usualy after 5-10 minutes theres enough heat to prevent this.


everything else is just an added benefit that keeps the greenies happy.
Total bull. The boiling point of Propane , the predominant hydrocarbon in LPG has a boiling point of - 32C, so with an ambient temperature of say 0C there is still 32C of heat going into the system, more than adequate to evaporate sufficient LPG to support combustion.
The freezing point of Propane is - 188C. When you have a converter ( gas heater) freeze up, it is atmospheric moisture freezing, generally indicating that the flow of water through the converter has failed. ie the temperature has fallen below 0C
I have spent most off my professional life working with LPG, and a considerable part of that time inspecting & approving LPG automotive conversions .
If your engine is equipped with an adequate ignition system it will start on straight gas without drama

[Blknight.aus]

:eek:

drive gently until the temp gauge is off the bottom stop,

if you cant start it and nail it from cold (even if you have to set a manual choke) without the engine baulking you....



If your engine is equipped with an adequate ignition system it will start on straight gas without drama

I'm going to assume you've heard the name lucas before today right?

[bee utey]

if you cant start it and nail it from cold (even if you have to set a manual choke) without the engine baulking you....

:p I genuinely don't care how brutally you treat cold engines. That's your lookout. If I have to wait for a couple of minutes at fast idle before I tow the big trailer out of my steep drive, I don't feel I'm in any way disadvantaged. Without a load there's ample power available to get me out to the main road at 60km/h by which time the temp needle is up and I can shoot off as hard as I like :burnrubber:.

[chopper]

Mixer type dual fuel systems on EFI vehicles generally start with a short burst of petrol. If they don't start well on LPG the petrol timer is likely out of adjustment or incorrectly set up. Running a dual fuel engine on petrol when cold is only shortening its life. Rings don't need bedding in each morning. My wife's old P76 did 400,000km on straight LPG and still has perfect compression figures. It also started easily when cold every day because of the right choice of high energy ignition and plug gap adjustment.

What do you do with the gap and heat range for gas ?

[bee utey]

What do you do with the gap and heat range for gas ?
Plugs 1 step colder heat range than stock setting or even 2 steps if its straight gas, gap around 30% smaller than the book figure, or around 0.7 - 0.8mm for a high energy ignition, 0.6mm for points or cars that easily backfire.